Conventionally, for example, in automobile electric components such as automobile lamps and ECUs (Electrical Control Units), OA (office automation) equipment, household electric appliances, and medical devices, a housing containing an electric component or a control board is provided with an opening for the purpose of reducing pressure variation in the housing caused by temperature change or allowing replacement of air in the housing, and a ventilation member is attached to the opening. The ventilation member ensures ventilation between the inside and outside of the housing, and also prevents foreign matters such as dust and water from entering the housing. Examples of such a ventilation member are disclosed in Patent Literatures 1 and 2.
For example, Patent Literature 1 discloses a ventilation member 101 as shown in FIG. 10 and FIG. 11. This ventilation member 101 is composed of a tubular body 102 made of rubber, a tubular cover component 103 having a bottom, and a gas-permeable membrane 110. The tubular body 102 has a slightly smaller diameter than the cover component 103, and the gas-permeable membrane 110 is disposed so as to close one opening of the tubular body 102. The tubular body 102 is fitted into the cover component 103 by inserting the portion of the tubular body 102 on the gas-permeable membrane 110 side into the cover component 103. Thus, a gas passage 104 is formed between the inner peripheral surface of the cover component 103 and the outer peripheral surface of the tubular body 102 and between the bottom surface of the cover component 103 and the gas-permeable membrane 110. The tubular body 102 made of elastically deformable rubber is press-fitted on a projecting portion 150b provided on the outer surface of the housing 150, and thus the ventilation member 101 can be attached to the housing 150 so as to cover the opening portion 150a of the housing 150.
As shown in FIG. 12 and FIG. 13, a ventilation member 201 disclosed in Patent Literature 2 includes a support body 202 on which a gas-permeable membrane 210 is disposed, and a cover component 203 fitted to the support body 202 so as to cover the gas-permeable membrane 210. A plurality of opening portions 203a are formed in the top or side of the cover component 203. A gas having permeated the gas-permeable membrane 210 passes through the opening portions 203a of the cover component 203, as a result of which ventilation between a space inside a housing 250 and a space outside the housing 250 can be ensured. The support body 202 has a base portion 202a and leg portions 202b extending from the base portion 202a. In this ventilation member 201, when the leg portions 202b are inserted into the opening portion 250a of the housing 250 via a sealing member 205, the leg portions 202b inserted in the opening portion 250a are elastically deformed to fix the ventilation member 201 to the housing 250. Conventionally, porous polytetrafluoroethylene (PTFE) membranes are often used as the gas-permeable membranes 110 and 210.